Synthesis, crystal structure and magnetic properties of novel heterobimetallic malonate-bridged MIIReIV complexes (M = Mn, Fe, Co and Ni)

Abstract

Five novel Re^IV–M^II bimetallic complexes of formula [ReCl₄(µ-mal)M(dmphen)₂]·MeCN [M = Co (1), Fe (2) and Ni (3)], [ReCl₄(µ-mal)Ni(dmphen)(MeCN)₂(H₂O)]·(MeCN)_0.5(H₂O)_0.5 (4), and [ReCl₄(µ-mal)Mn(dmphen)(H₂O)₂]·dmphen·MeCN·H₂O (5) (mal = malonate dianion, dmphen = 2,9-dimethyl-1,10-phenanthroline) have been synthesized, and the structures of 1, 2, 4, and 5 determined by single-crystal X-ray diffraction. The structures of 1 and 2 consist of neutral [ReCl₄(µ-mal)M(dmphen)₂] dinuclear units where the metal ions are linked through a malonate ligand which adopts simultaneously the bidentate (at Re^IV) and monodentate (at M^II) coordination modes. The bridging carboxylate–malonate group in them exhibits the anti–syn conformation. The rhenium atom is six-coordinated with four chloro atoms and two carboxylate-oxygens from a bidentate malonate group in a distorted octahedral environment. The M atom is five-coordinated being surrounded by four nitrogen atoms of two bidentate dmphen ligands and one oxygen atom of the malonato ligand. There are also Re^IV(µ-mal)Ni^II dinuclear units in 4 with the same type of bridge, but the nickel atom is six-coordinated with one bidentate dmphen, two molecules of acetonitrile and one water molecule as peripheral ligands. Compound 5 is a neutral chain compound with regular alternating rhenium(IV) and manganese(II) ions. The [ReCl₄(mal)]²⁻ units in each chain act as bismonodenate ligands through two carboxylate-oxygen atoms toward [Mn(dmphen)(H₂O)₂]²⁺ entities. Variable-temperature magnetic measurements of 1–5 in the temperature range 2.0–300 K show the occurrence of weak antiferromagnetic interactions which are rationalized on the basis of the structural knowledge and simple orbital considerations. Very noticeable is compound 5, a ferrimagnetic chain with regular alternating Re^IV and Mn^II cations.